Imprint lithography has received attention as a possible alternative to conventional photolithography because of its ability to print small features at low cost. Step and flash imprint lithography is one kind of imprint lithography that is amenable to the resolution and overlay requirements necessary for the fabrication of advanced semiconductor devices. With step and flash imprint lithography, a photosensitive material is squeezed between a substrate and a mechanically rigid, ultraviolet (UV) transparent template having a relief pattern. The photosensitive material is then exposed to actinic radiation, causing it to cure in situ. The resulting cured, hardened layer, which has a pattern of features defined by the relief pattern, can be used as an etch mask to transfer this pattern into an underlying substrate.
Unfortunately, such a process is prone to a large number of defects, the primary sources of which are particles and cohesive failure of the cured material during debonding (see, for example, W. J. Dauksher et al., Proc. SPIE 6517, 651714, 2007). Cohesive failure occurs when the bond between the cured material and the template is stronger than the bonds within the cured material itself. For this reason, it is generally necessary to pre-coat the template with a release agent or coating, so that the template does not stick to the cured material. Unfortunately, release coatings are not necessarily effective and durable (see, for example, F. A. Houle et al., J. Vac. Sci. Technol. B 23, 2427, 2007). If a coating is ineffective, the cured material will become bonded to the coating as a result of the curing step, with the bond between the cured material and the coating being potentially as strong as, or even stronger than, what the bond would be between the cured material and the bare (uncoated) template surface. On the other hand, if a coating is not durable, its repeated contact (e.g., as in a step and repeat patterning process) with photosensitive material during the curing process will eventually result in its degradation. In both cases, patches of highly adhesive regions can eventually develop on the template surface to which the curable material can bind. These patches will create defects in the corresponding imprinted patterns, thus requiring the template to be either refurbished or discarded.
Fluorosilanes have been widely used as release agents, but tend to degrade over time when used with curable materials. Both an alkane silane film (specifically SAMLAY™ from Nippon Soda Co., Ltd, as reported by K. Kumazawa et al., Nanoprint Nanoimprint Technology Conference, San Francisco, 2006) and a diamond-like carbon film (see F. A. Houle et al., Appl. Phys. Lett. 90, 213103, 2007) have been shown to be as effective or even better than fluorosilanes when used with acrylate and methacrylate-based resists, respectively. However, diamond-like carbon does not work well with vinyl ether resists. All of these release agents are chemically vulnerable and subject to degradation with use.
Accordingly, there is a need in the art for improved release layers for templates used in step and flash imprint lithography.